Lock seam for helical corrugated pipe

ABSTRACT

A SEAM FORMED OF INTERLOCKED OPPOSITE MARGINAL SIDE EDGE PORTIONS OF A LONGITUDINAL CORRUGATED, RELATIVELY THICK, STRIP HELICALLY CURLED INTO CORRUGATED PIPE, WHICH SEAM IS WITHIN THE OUTSIDE AND INSIDE DIAMETERS OF THE PIPE AND THE BOUNDS OF A STANDARD CORRUGATED COUPLING.

March 23, 1971 P. K. DAVIS 3,572,394

LOCK SEAM FOR HELICAL CORRUGATEDIPIPE v Filed ov. 19, 1968 INVENTOR. P40; K, D4V/5 Irma/swim? United States Patent 3,572,394 LOCK SEAM FOR HELICAL CORRUGATED PIPE Paul K. Davis, Alameda, Calif., assignor to Pacific Roller Die Co., Inc., Hayward, Calif. Filed Nov. 19, 1968, Ser. No. 777,066 Int. Cl. F161 9/06, 9/16 U.S. Cl. 138-154 4 Claims ABSTRACT OF THE DISCLOSURE A seam formed of interlocked opposite marginal side edge portions of a longitudinaly corrugated, relatively thick, strip helically curled into corrugated pipe, which seam is within the outside and inside diameters of the pipe and the bounds of a standard corrugated coupling.

BACKGROUND OF THE INVENTION This invention relates to corrugated pipe helically formed of an elongated strip of sheet metal, and more particularly, to seams for interlocking the opposite side edges of said strip.

A known method of fabricating sheet metal pipe having helical or spiral corrugations involves the steps of initially forming a series of longitudinally extending corrugations in an elongated sheet metal strip, curling the strip into helical convolutions, and then joining the opposite side edges of the curled strip at a seam formed of scam element which are hook-shaped in cross-sectional contour and in interlocking relationship, such seam being termed a lock seam.

The corrugations of the metal strip comprise alternating ridges and valleys and intervening connecting portions. Such corrugations may be defined in terms of a corrugation pitch, which is the distance between two adjacent ridges, and a corrugation depth, which is the distance between a ridge and a valley in the direction perpendicular to the plane of the strip. The corrugation neutral axis extends in parallel relationship to the plane of the strip through points equidistant the ridges and valleys.

Conventional forms of lock scam in pipe are provided by interlocking a pair of oppositely directed hook-shaped seam elements, which pair of elements are variously centered at the corrugation ridge or valley, or midway between a ridge and adjacent valley. Centering the seam at a ridge or valley is undesirable since stress is greatest at the ridges and valleys when the pipe is subjected to loads which tend to flatten the corrugations. It is, therefore, preferable to center the seam at or near the neutral axis of the corrugation, where stress is a minimum.

The above-noted forms of conventional lock seam have proven unsatisfactory in some applications. For example, it is frequently desired to employ band-type pipe couplings, of either the flat band type or the form having corrugations which match the corrugations of pipe sections to be coupled. The known forms of lock seam present outwardly protruding portions which interfere with optimum seating of the corrugated-type of band coupling, and in cases where seam portions protrude beyond the outer surface of the normal corrugation ridge, there is interference with seating of the fiat band coupling. In some instances, the thickness of the metal strip relative to the corrugation pitch and depth is sufficiently great that the 3,572,394 Patented Mar. 23, 1971 ice SUMMARY OF THE INVENTION The lock seam constructed in accordance with this invention is centered at a point substantially lmidway between an adjacent pair of corrugation valleys at or near the corrugation neutral axis and is confined to a crosssectional area that does not extend outwardly of the outer surface of the corrugation nor inwardly of the inner surface of the corrugation valleys. It provides a high strength seam in which, as contrasted with conventional lock seam, severity of bends is reduced and objectionable protruding seam portions are eliminated. Further, it is readily formed in heavy gauge strip material wherein the thickness of the material is sufficiently great relative to the corrugation pitch and depth that a conventional lock seam cannot practically be formed.

It is therefore an object of this invention to provide a novel, high strength lock seam for helically corrugated sheet metal pipe, which does not interfere with optimum seating of band-type pipe couplings.

Another object of the invention is the provision of a pipe lock seam especially seated for use in helically cor rugated sheet metal pipe of the heaviest gauges of sheet material employed in corrugated pipe formation.

Other objects and advantages will become apparent from the following description of the preferred forms of the invention, which are illustrated in the drawings accompanying and forming part of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view of portions of two sections of helically corrugated pipe having one form of lock seam embodying this invention, joined together by a corrugated band-type coupling;

FIG. 2 is a cross-sectional view taken along line 2-2 of FIG. 1;

FIG. 3 is an enlarged fragmentary cross-sectional View of the lock seam of FIG. 1 and associated strip and band coupling portions, taken substantially along line 3-3 of FIG. 1;

FIG. 4 is a fragmentary sectional view, similar to FIG. 3, of a modified form of pipe lock seam embodying the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In detail, a preferred form of lock seam of this invention is illustrated in FIGS. l-3. In FIG. 1 strips of longitudinally corrugated sheet metal have been helically curled, and the opposite side edges thereof interlocked at a seam, generally designated 3. The corrugations of the resulting pipe sections 4, 5 define alternating ridges 10 and valleys 11 with respect to the outer surface of the pipe. In cross-section (FIG. 3, in which the pipe outer surface is uppermost) seam 3 is centered midway between a corrugation valley 6 in the marginal edge portion 7 adjacent side edge 8, and a corrugation valley 9 in the marginal edge portion 12 adjacent the opposite side edge 13. Nearest edge 8 the marginal portion 7 includes a seam element 14 of generally U-shaped cross-section,

and correspondingly, nearest edge 13 marginal edge portion 12 includes an oppositely opening similar seam element 15. Seam elements 14 and 15 are in lapped, interlocked relation, and the end flange or first seam part 16 of scam element 14 and the end flange or first seam part 17 of scam element 15 are in face-to-face contact. At the cross-section, all points of contact between flanges 16 and 17, indicated at 18 at FIG. 3, lie along the corrugated neutral axis 19. A second seam part 20 connected to flange 16 is in engagement with the opposed face of flange 17, and a second seam part 21 connected to flange 17 is in engagement with the opposed face of flange 16.

Between valley 6 and seam element -14 extends a connecting portion 22 which includes a curved heel portion or third seam part 23 in engagement with the closed end 24 of seam element 15. The connecting portion 25 extends from valley 9 generally parallel to the corrugation neutral axis to a heel portion or third seam part 26 in engagement with the closed end 27 of seam element 14. Heel portions 23, 26 preclude relative movement of seam elements 14, 15 from the interlocked position.

For joining pipe sections 4, 5 (FIG. 1), it may be desired to employ a conventional band coupling 28 (FIGS. 1 and 2) comprising a band 29 (FIGS. 1-3) having corrugatio-ns matching those of pipe sections 4, 5 (FIG. 1), and fastener means 32 (FIGS. 1, 2) by which the overlapped ends of band 29 are drawn together for firmly engaging said band around the joined pipe sections. Coupling 28 is in optimum position for most effectively securing pipe sections 4, 5 against relative axial and circumferential movement when all of the corrugations of band 29 are in contact with corresponding corrugations of the pipe sections. This requires that the pipe surface be free of projections and irregularities that extend outwardly of the corrugation contour. Seam 3 (FIGS. 2, 3) is disposed fully within the corrugation contour for eliminating interference with such optimum seating of the corrugated band 29.

The modified seam of FIG. 4 has seam elements 33, 34, respectively corresponding to seam elements 14, 15 of FIG. 3. Seam 30 is similar to scam 3 in that it is centered at a point midway between adjacent corrugation valleys 35, 36 and on the corrugation neutral axis, indicated at 37, and includes flanges 38, 39 parallel to neutral axis 37. However, in the connecting portion 42 between valley and seam element 33, and in the connecting portion 43, between valley 36 and seam element 34 bends are eliminated so that connecting portions 42, 43 are substantially flat. Connecting portion 43 does, however, provide a heel portion 44 in engagement with the end 45 of seam element 34 by virtue of its angular disposition relative to the corrugation neutral axis. As with seam 3, seam 30 is fully within the corrugation contour to eliminate interference with optimum seating of a corrugated band coupling, indicated in broken line at 29'.

It is to be noted that since both lock seam forms 3, 30 are centered between adjacent corrugation valleys, they may occupy a space substantially equal to the full corrugation pitch. Bends, such as heel portions 23 and 27 of seam 3 (FIG. 3) will not be as severe as corresponding bends in a seam formed in accordance with conventional practice, i.e., between a ridge and adjacent Walley, occupying a space equal to one-half the corrugation pitch. Reducing the severity of bends avoids sharp angles which weaken sheet metal material and interrupt the protective coating, such as the zinc coating of galvanized steel material commonly used in forming corrugated pipe. In some instances in which heavy gauge sheet material is utilized and corrugations are provided in standard contours, a space equal to one-half the corrugation pitch is insuflicient to accommodate a lock seam. For example, in forming pipe having a diameter of thirty-six inches or greater, eight gage (approximately 0.165 inch thick) or ten gage (approximately 0.135 inch thick) sheet material is utilized and normally formed with a standard corrugation having a pitch of two and two-thirds inches and a depth of one-half inch. For such pipe the thickness of the strip material is between approximately one-third and one-fourth the depth of corrugations and the pitch of the corrugations is of the order of five times the depth. The seam of this invention is well adapted for use in pipe having such dimensions.

It is to be understood that the claims appended hereto are intended to cover all changes and modifications of the examples herein chosen for purposes of disclosure which do not depart from the spirit and scope of the invention. For example, it is not essential to this invention that the seam include heel portions, as exemplified by portions 23, 26 of FIG. 3. Further, the seam may be centered to one side of the midway point between two adjacent corrugation valleys or inwardly or outwardly of the corrugation neutral axis a distance less than one-half the depth of the corrugations and still yield a seam that is fully within the normal corrugation contour.

I claim:

1. In pipe formed of a helically elongated strip of sheet material having longitudinally extending uniform corrugations with outer surfaces all of uniform surface contour providing alternating ridges and valleys and intervening connecting portions relative to the outer surface of said pipe a seam for joining the opposite side edges of said strip, comprising:

(a) a first seam element of generally U-shaped crosssection formed along one marginal edge portion of said strip and having a curved closed end;

(b) a second seam element of generally U-shaped crosssection formed along the opposite marginal edge portion of said strip and having a curved closed end;

(c) said first and second seam elements being in interlocked relationship;

(d) a generally flat end flange on each of said seam elements;

(e) said end flange on said first seam element and said end flange on said second seam element being in mutual contact substantially midway between a first valley in said one marginal edge portion and an adjacent valley in said opposite marginal edge portion at a plane spaced outwardly of said first and adjacent valleys a distance no greater than substantially one-half the depth of said corrugations; and

(f) all portions of said first and second seam elements being located with respect to the outer surface of said pipe to be within the bounds of a surface extending between said first valley and said adjacent valley and having the contour of said outer surface of one of said uniform corrugations.

2. The seam of claim 1, wherein:

(f) said plane of mutual contact is substantially at the neutral axis of said corrugations.

3. The seam of claim 1, including:

(f) a connecting portion extending between said valley in said one marginal edge portion and said first seam element and having a surface in contact with said closed end of said second seam element.

4. In pipe formed of a helically elongated strip of sheet material having longitudinally extending corrugations providing alternating ridges and valleys and intervening connecting portions relative to the outer surface of said pipe a seam for joining the opposite side edges of said strip, comprising:

(a) a first seam element of generally U-shaped crosssection formed along one marginal edge portion of said strip and having a curved closed end;

(b) a second seam element of generally U-shaped crosssection formed along the opposite marginal edge portion of said strip and having a curved closed end;

(c) said first and second seam elements being in interlocked relationship;

(d) a generally fiat end flange on each of said seam elements;

(c) said end flange on said first seam element and said end flange on said second seam element being in mutual contact substantially midway between a first valley in said one marginal edge portion and an adjacent valley in said opposite marginal edge portion at a plane spaced outwardly of said first and adjacent valleys a distance no greater than substantially one-half the depth of said corrugations;

(f) a connecting portion extending between said valley in said one marginal edge portion and said first seam element and having a surface in contact with said closed end of said second seam element; and

(g) a second connecting portion extending between said valley in said opposite marginal edge portion and said second seam element and having a surface in engagement with said closed end of said first seam element.

References Cited UNITED STATES PATENTS 3,094,147 6/1963 Nemer 1381S4 3,447,352 6/1969 Miller 285-424 3,455,584 7/1969 Hendrickson 138154 10 DOUGLAS HART, Primary Examiner U.S. Cl. X.R. 

